SILVER SCURF

Helminthosporium solani, fungus; no foliar disease

Infection:

The principle method of infection is believed to be through infected seed. Infected seed release silver scurf into the soil where it can survive for up to six months and infect new tubers. Silver scurf may spreads in storage when temperature is above 40 F and humidity is 90-95%. Reports have indicated that silver scurf can spread in storage through the ventilation system. Silver scurf has also been reported to be able to survive in storage facilities on wood, sheet metal and insulation. Spread is minimal but progresses severely on an infected tuber in storage.

Symptoms:

Tubers need to be washed to observe symptoms of silver scurf. When tubers are slightly or initially infected, small, round, shiny, light brown spots appear at the stem end. With greater infection or as disease spreads on tuber, the skin has large areas with a shiny silvery appearance. This can be difficult to detect on white-skinned and easily detected on red-skinned varieties. A fluorescence may appear under a black light. With storage, the blotches may wrinkle. No rot is associated with silver scurf; there is no internal symptoms. Silver scurf can readily be confused with black dot and laboratory observations are needed.

Control Practices:

Don't let tubers over-mature before harvest. Don't harvest under wet conditions. Keep tubers dry, cool and well ventilated. Silver scurf does not like humidity below 90%. Thiabendazole applied to tubers going into storage is reported to inhibit silver scurf, but resistance has been widely reported. EBDC seed treatments applied to tubers in storage has been reported to be effective. Fludioxonil was registered as a seed treatment for controlling silver scurf in 1997.

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